The invention relates to a device for measuring mechanical states of stress in components and, in particular, to a device for measuring mechanical states of stress in components wherein a part of the device is nonpositively joined to the component whose mechanical states of stress are to be measured. The part of the device undergoes a change in a measurable variable in the event of a change in the mechanical states of stress.
A device of the generic type is already known and is generally referred to as a strain gauge. These strain gauges are described, for example, in the German book entitled: Meyer's Lexikon der Technik und der exakten Naturwissenschaften (Meyer's Lexicon of Engineering and the Exact Sciences), Bibliographisches Institut AG, Mannheim 1969, to the effect that a resistance wire is glued in loop or zigzag form to a paper or plastic strip as a substrate. The strain gauge obtained in this manner is then glued onto an object to be measured. The length and the cross section of the resistance wire and, consequently, also the resulting resistance then change as a result of expansions or contractions of the object to be measured. Expansions or contractions of the object to be measured are deduced from this change in resistance.
In the device hitherto known, disadvantages arise to the effect that the resolution of the strain gauges is limited by the fact that the strain gauges are only glued on to the object to be measured. The resolution is then limited by the fact that small expansions or contractions which are not transmitted by the glue layer can also not be detected.
There is, therefore, needed a device for measuring mechanical states of stress in components in such a way that the device has as high a response sensitivity as possible and, at the same time, operates as independently as possible of the ambient conditions.
According to the invention, these needs are met by a device for measuring mechanical states of stress in components wherein part of the device is nonpositively joined to the component whose mechanical states of stress are to be measured and the part of the device undergoing a change in a measurable variable in the event of a change in the mechanical states of stress. The part of the device is a layer which is deposited on the component by atomic growth. The part has a layer structure containing less than 8% by weight of phosphorus, preferably up to 3% by weight of phosphorus, up to 2% by weight of an element of main group IV or V, in particular antimony or lead, and up to 5% of a transition metal element, in particular cobalt or iron. The percentages by weight resulting from the sum are increased to 100% with nickel. The layer modifies the magnetic flux in a coil arrangement comprising at least one coil. This change in the magnetic flux in the coil arrangement is evaluated and the mechanical state of stress of the component is deduced from the change in the magnetic flux.
Further advantages of the invention compared with the known prior art are that the device according to the invention has only a low overall height on the object to be measured.
Ceramic materials which are used, for example, in turbocharger rotors or valves in motor-vehicle construction have a high mechanical rigidity. If stresses are to be measured, problems occur to the effect that the mechanical stresses result only in small changes in length because of the high mechanical rigidity. These small changes in length can be measured with surprisingly good resolution by amorphous or nanocrystalline layers which are deposited directly on the component and have a high magnetoelasticity.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.